Today, the need for alternative energy sources is a central concern because of traditional resource depletion and global climate change due to emission of greenhouse gases. Hydrogen is an apparent alternative to hydrocarbon fuels. It has been proposed as a means to reduce greenhouse gases and other harmful emissions, satisfying the need of efficient, sustainable, non-polluting source of energy. It is an ideal energy carrier that helps to increase our energy diversity and security by reducing our dependence on hydrocarbon-based fuels.
Hydrogen is produced from a very diverse base of primary energy feedstocks and a variety of process technologies including steam reforming, partial oxidation, coal gasification, biomass pyrolysis/gasification, electrolysis, photosynthetic/photobiological, photocatalytic water splitting and thermochemical water splitting.
Hydrogen production from water splitting is environmentally benign and attractive as a clean source of energy. Thermochemical process for hydrogen production utilizing water as a raw material and nuclear energy as primary energy source is an attractive option which involves the separation of water into hydrogen and oxygen through chemical reactions at high temperatures to create a closed loop where water can be fed to the process; and all other reactants are regenerated and recycled.
More than hundred thermochemical cycles have been reported in the literature. A few of the most promising cycles have been studied so far based on some criteria as simplicity of the cycle, efficiency of the process and the ability to separate a pure hydrogen product. Among various feasible thermochemical cycles i.e. sulphur-iodine, cerium-chlorine, iron-chlorine, vanadium-chlorine and copper-chlorine, Cu—Cl cycle has the advantage to produce required hydrogen at a relatively low temperature (550° C.).
Cu—Cl cycle is a hybrid process which uses both heat and electricity to carry out a series of reactions i.e. chemical and electrochemical reactions where the net reaction is the splitting of water into hydrogen and oxygen. The proposed Cu—Cl cycle has two variations, which are known as a four-step process and a five-step process. There are some technical challenges associated with Cu—Cl cycle. Despite these challenges and risks, the Cu—Cl cycle offers a number of key advantages.
GB1461646 discloses a process for production of water by an endothermic cycle through intermediate copper-chlorine and magnesium compounds where intermediary products react and are regenerated.
U.S. Pat. No. 3,919,406 describes a closed loop thermochemical route for production of hydrogen by a succession of four reactions where chlorides of copper and magnesium, hydrochloric acid, and magnesium oxide break down water into its constituent elements with a net result of splitting water into hydrogen and oxygen.
US2008/0256952 discloses a solar powered thermochemical Cu—Cl hydrogen production system and a solar heating system with molten salt comprising sodium nitrate and potassium nitrate, as a heat transfer medium to provide thermal and electrical energy to the thermochemical, system.
US2010/0129287 describes a system for production of hydrogen gas from water decomposition using a thermochemical cycle comprising three, four and five steps. The present invention relates to reactors and vessels and heat coupling methods which are used in a closed loop of a copper-chlorine thermochemical cycle to produces hydrogen and oxygen by using energy from clean sources such as nuclear and solar.
US2010/0025260 discloses a new approach to use low grade heat or waste heat from nuclear or an industrial sources for hydrogen production using combined chemical or vapor compression heat pumps and a thermochemical cycle.
Barbooti et al. (Thermochimica Acta 78 (1984) 275-284) have explained the copper-chlorine thermochemical cycle involving the set of reactions such as hydrogen production, partial regeneration of copper, dechlorination of copper chloride, generation of oxygen and regeneration of hydrogen chloride.
Lewis et al. (Nuclear Production of Hydrogen, Third Information Exchange Meeting, 2003) have developed low temperature cycles designed for low temperature heat around 500 to 550° C.
Rosen et al. (Canadian Hydrogen Association Workshop, 2006) have focused on a copper-chlorine (Cu—Cl) cycle, which has been identified as a highly promising cycle for thermochemical hydrogen production driven by nuclear heat from Super-Critical Water Reactor (SCWR).
Lewis et al. (Int. J. Hydrogen Energy 34(9) (2009) 4115-4124 and 4125-4135) have carried out a detailed study of thermochemical cycles for efficiency calculations.
Orhan et al. (Int. J. Hydrogen Energy 35 (2010) 1560-1574) have studied the coupling of Cu—Cl thermochemical cycle with a desalination plant for nuclear-based hydrogen production.
Rosen et al. (Canadian Hydrogen Association Workshop, 2006) have focused on a copper-chlorine (Cu—Cl) cycle, which has been identified as a highly promising cycle for thermochemical hydrogen production driven by nuclear heat from Super-Critical Water Reactor (SCWR).
Daggupati et al. (Int. J. Hydrogen Energy 35(10) (2010) 4877-4882) have examined copper chloride solid conversion during hydrolysis to copper oxychloride in the thermochemical copper-chlorine (Cu—Cl) cycle of hydrogen production.
Serban et al. (AIChE 2004 Spring National Meeting, 2004) has adopted an approach of seeking water-splitting cycles that have maximum reaction temperatures of less than 550° C. This makes it possible to consider a number of lower temperature nuclear reactors, including supercritical water and liquid metal cooled reactors as well as high temperature CANDU reactors.
Cu—Cl cycle presents a number of prospective advantages such as maximum cycle temperature (550° C.) allow the use of a wider range of heat sources like nuclear, solar etc; intermediate chemicals are relatively safe, inexpensive and abundant. This involves minimum solid handling as compared to other processes which allows the cycle to operate efficiently. All individual steps have been investigated and experimentally proven. One of the steps could be performed at a much lower temperature by use of low grade waste heat from the nuclear or other sources. Though, ahead of these advantages can be recognized, scale-up of equipment is needed further.